Intrathecal Baclofen In the Treatment of Adult Spasticity

Joseph C. Hsieh, M.D., M.B.A., M.P.H.; Richard D. Penn, M.D.

Disclosures

Neurosurg Focus. 2006;21(2) 

In This Article

Risks

Several risks are involved with placement of baclofen pumps. Stempien and Tsai[35] published perhaps the single most comprehensive study of ITB complications in a survey of 40 centers with a total experience of 1002 test doses and 936 pump placements. Common test-dose complications were nausea/vomiting (2.6%) and sedation (2.2%). Pump complications included CSF collection (3.3%), constipation (2.9%), and headache (2.4%). Common long-term complications were catheter kink or migration (4%) and in fection (1.2%).

Even with safe surgical techniques, some common com plications of baclofen pump placement still occur. Ex cessive swelling may be a sign of a developing seroma, sometimes requiring percutaneous drainage. A CSF leak may be detected by a spongy swelling around the incision site, sometimes characterized by a ripple effect when tap ped. Standard measures to reduce local CSF pressure at the level of the defect, such as having the patient lie flat without a pillow, are often sufficient. Other measures in clude using a blood patch and/or abdominal binder.

In the product manual, Medtronic warns of specific risks related to the pump itself. For instance, heating of local tissue in circumstances such as short-wave dia thermy within 30 cm of the pump or catheter has been shown to elevate temperatures and cause baclofen overinfusion. Sour ces of electromagnetic interference like magnetic resonance imaging will temporarily stop the pump motor's ro tor due to the magnetic field of the imager, leading to brief disruption of intrathecal therapy. Furthermore, in creases in environmental pressure have been found to lead to slower infusion rates. Therefore, a patient must be warn ed before participating in activities such as scuba diving. Con versely, lower pressures will lead to higher infusion rates. Patients participating in extended high-altitude ac tiv ities or stays may therefore require readjustment.

A special note should be made about the risks of infection. Normal hallmarks of infection such as warmth or red ness around the incision site should be observed and monitored closely. More ominous signs, such as purulent drainage, should be dealt with on an emergency basis, be cause severe infections may lead to meningitis. Pump removal and intravenously administered antibiotic drugs appropriate for the infecting bacteria are then indicated. In general, infection rates for baclofen pumps implanted to deliver the drug in an effort to treat spasticity appear to range from 0.7 to 1.7%.[30,35] Meningitis in patients with implanted pumps ranges from 0 to 0.7%.[28] Infections of the pump rather than the reservoir or catheter appear to be most prevalent in the literature. Reported infections ap pear to involve the perioperative period after placement of the pump. The most common offending bacteria are Staph y lo coccus aureus or S. epidermidis. Repeated percutaneous refills appear to carry little risk of infection. One theory suggests that the host-derived albumin coating of the pump pocket reduces the risk of colonization.[37] There are also reports of colonization of implanted pump reservoirs by bacteria and fungus without clinical infection.[31]

Intrathecal use of baclofen does not completely eradicate the central risks. The most frequent drug-related side effects of ITB include drowsiness, dizziness, constipation, and muscular hypotonia.[4] A bolus dose that is too high can result in rostral progression of hypotonia, followed by brainstem toxicity as the baclofen is carried up the neuraxis by rostral bulk CSF flow. Brainstem effects include respiratory depression, hypotension, bradycardia, and co ma. Continuous infusion generally has a safer profile than bolus infusion. Malfunctions in prototype pumps have also been noted in the literature, resulting in milli gram levels of ba clofen release and leading to coma, al though newer pump models have not shown this defect.[27]

In cases of severe overdose, the pump should be stop ped immediately. Simple airway, breathing, and circulation considerations must be addressed, with mechanical ventilation, intravenous fluids, and vasopressors as supportive measures. Pump interrogation is preferred if a programmer is available. In cases in which pump malfunction is the cause, the device should be turned off if necessary. A 20-ml sy ringe and 22-gauge Huber needle may be used for access to the fill port for removal of medication. In cases in which the acute overdose is caught within a few hours of the event, a withdrawal of 30 to 40 ml of CSF through the catheter access port may remove the most concentrated baclofen in the CSF (high-volume lumbar puncture has a similar effect). Cases identified beyond this time window are not amenable to CSF removal because the drug has already undergone diffusion and flow up the spinal canal. Although baclofen has no direct antagonist, drowsiness and respiratory depression may be reversed with 1 to 2 mg of intravenous physostigmine over 5 to 10 minutes.

Baclofen withdrawal is a serious risk if there is an ab rupt decrease in drug infusion. Causes include catheter failure (for example, obstruction, fracture, or dislodging of the intrathecal catheter), pump malfunction, or low pump re serves. Symptoms include pruritis without a rash, diaphoresis, hyperthermia, hypotension, chan ges in mental status, and aggravation of spasticity. Continued withdrawal may result in rhabdomyolysis or multiple organ failure, or it may mimic autonomic dysreflexia, sepsis, ma lignant hy perthermia, or neuroleptic–malignant syndrome. Manage ment involves adequate evaluation of recent painful stimuli, listening for pump alarms, pump interrogation, ab do minal and/or spine x-ray films, or indium infusion studies to evaluate for catheter fracture and baclofen ex travasation. Once a diagnosis is made, oral bac lofen may be administered if tolerated. In severe withdrawal, intra thecal baclofen administration through lumbar puncture may be necessary. Additional intravenous benzodiazepine therapy titrated according to effect may prove useful.

Although they are uncommon, the risk of baclofen-re lated seizures deserves a special discussion. Inter esting ly, both overdose and withdrawal of baclofen appear to in duce seizures, especially in cases of supraspinal spasticity. Rates of seizure activity in patients receiving boluses of intrathecal baclofen are as high as 10.3% in cases of spasticity with supraspinal origin.[15] Overdose-related seiz ures may be caused by rostral baclofen bulk flow to supra spi nal tissue. Withdrawal seizures may occur as baclofen is eliminated from lipid stores and brain tissue.[9] The seemingly paradoxical anti- and proconvulsant ef fects of ba clofen may depend on the location of GABAB–re lated in hi bition (for example, on excitatory or inhibitory neurons in traumatized neuronal tissue). In each case, sudden drug level changes seem to have been most critical in the seizure-related activity.

Tolerance is another risk that deserves special attention. Several factors may require progressively higher doses of ITB. Tolerance necessitates increasing doses of medication, but it can be limited on occasion by a drug holiday. Some centers report success with intrathecal morphine during this holiday. Others have used intrathecal fentanyl, although it has not been approved by the Food and Drug Administration for this indication.[8] Progressive disease, decubitus ulcers, and infections (urinary or systemic) may also require readjustment of dosing.

Comments

3090D553-9492-4563-8681-AD288FA52ACE
Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.

processing....